This invention relates to a meter testing device, particularly an electric watt-hour meter. The invention is particularly concerned with verifying the operational accuracy of such watt-hour meters.
Electricity supply companies are often requested by users of electrical power to ascertain and prove the accuracy of the watt-hour meter which reads the amount of electricity being consumed by the custumer. To satisfy such customers the utility companies send a skilled testman to the operational site and through fairly complex operational techniques the meter accuracy is tested. It is recognized that the accuracy of the meter is within a standard of error of 2%, and in the event of the meter being inaccurate to a degree greater than this, then procedures have to be followed at the operational site to have the meter rectified.
At manufacturing and laboratory locations electric watt-hour meter testing and calibration require skilled, technical operators who operate highly sophisticated and complex equipment, and it is clearly not feasible to use such equipment at different operational sites.
Inherently, therefore, it is desirable to provide a watt-hour meter testing apparatus and a method for testing such meters which is relatively simple by nature, so that verification at the operational site can be made by relatively unskilled testmen or meter readers. At the same time the testing apparatus should be able to provide the user at the operational site with simple verifiable evidence as to the accuracy or otherwise of the meter under test. None of this is to date possible with the known meter testers and methods of determining accuracy.
In U.S. Pat. No. 4,271,390 (Canu), there is disclosed a meter testing device wherein an adapter is inserted into a meter receiving socket and the meter under test is then fitted into the adapter. With the adapter are means for measuring the volts or wattage passing through a known load in the form of a standard light bulb connected to the adapter, the voltage and wattage being displayed. A comparison therefore of the displayed wattage relative to the bulb's rated power characteristics is the indication of the accuracy of the meter. With this device, however, the power supply lines are isolated from the normal operational load and this leads to inconvenience at the operational site. Additionally the load in the form of a standard light bulb is relatively very low compared to the normal operational load and thus read by the meter. Thus the degree of accuracy obtained by this prior art device is not representative of normal conditions and is thus relatively poor.
In U.S. Pat. No. 2,249,075 (Young), there is disclosed an adapter which can be interposed between a meter socket and a meter and to which a suitable measuring instrument can be connected. This device however does not indicate that the device could be used for loading the meter in any way and/or obtaining a verification of the meter.
In U.S. Pat. No. 2,938,165 (Greig), there is disclosed the standard method for testing meters in a laboratory whereby a standard meter and a meter under test are effectively connected with a loading transformer with different loading situations. This complex testing procedure requires two meters: the standard meter puts out pulses according to the revolutions of the meter disc, and the meter under test likewise puts out pulses according to light passing through an aperture of its revolving disc. The relative pulse counts are compared and a reading of accuracy is obtained in the form of indicating the percentage registration of the meter under test. The test disclosed in this patent requires that the speed ratios of the standard meter and tested meter are the same. Accordingly, different standard meters are required to test different meters being verified. The application of the disclosed test is therefore limited to specific apparatus. The photo pickup which is used to pass light through the appurture in the meter under test is suitable for operation under laboratory conditions. However, this photo pickup method has never been found applicable in practice in the prior art for use at outdoor operational sites since there are ambient light conditions which impact greatly on the light between the generating source and receiving means thereby affecting the signal picked up by the receiver. Consequently, to date it has been necessary to count revolutions of the disc in the field simply by visibly detecting a black mark on the outer perimeter of the disc and physically counting the number of revolutions by counting the number of times that the dot passes. This is susceptible to inaccuracies.
A sample of prior art known for calibrating a watt-hour meter in a laboratory exists in U.S. Pat. No. 3,409,829 (Elmore), where there is disclosed a computer controlled callibration test rack and from which it is clear that laboratory testing of meters is complex and not amenable to use in operational sites by relatively skilled testmen.
U.S. Pat. Nos. 4,120,031 (Kincheloe), 4,133,034 (Etter), 4,224,671 (Sugiyama), 4,240,149 (Fletcher), and 4,283,772 (Johnston) disclose various forms of electronically monitoring and calculating characteristics associated with power usage through watt-hour meters.
In the commercial field, E. J. Brooks Company of Michigan markets a meter evaluator under the trade name EKSTROM wherein the evaluator places a high load on the meter and a fixed number of revolutions of the meter disc is timed. Calculations are then made by inserting the time interval into a percentage registration formula and then determining the percentage of registration of the meter. The load applied to the meter is in the form of two hair drier type motors and heating coils, and thus this is a noisy test device and heavy on its loading requirements, thus producing excessive heat.
Another commercially available system is that produced by System Jett of North Carolina who provide a Calibration Checker, model SJ621, which requires inserting an adaptor with a standard meter and a meter under test into the meter receiving socket. Simultaneously electronically comparing the readings through the meters are obtained such that the kilowatt hours of each meter are obtained, and also the percentage registration of the meter under test is ascertained.
In the tester known commercially as the "The Average Beast", H. J. Arnett Industries, Inc. of Portland, Ore. places an adaptor into the meter socket and then puts the meter into the adaptor. After timing a predetermined number of disc revolutions, readings are compared against a tabulated set of figures to ascertain the percent registration of the meter. In the application of this verifier the power between the line and operational load is broken, and additionally the disadvantage of manual calculation is necessary.
In yet a further commercial device, the ACCU-VER verifier marketed by Custom Terminals Corp. of Hauppange, New York locates an adaptor between the meter receiving socket and the meter and then applies a test with a known load to the meter. Thereafter after timing the meter disc for one or more revolutions, there is obtained a rough accuracy check.
None of the cited art however provides for meter verification which is simple to apply by non-skilled personnel at an operational site, nor does any apply a representative real load to the meter such that verification under normal operating conditions can be obtained.
Furthermore, the prior art does not disclose of an effective light generating and receiving means which is operational with a rotating disc of the meter whereby accurate determinations of the watt-hours in the meter can be made at the operational site. Also non-existent in the prior art is the means of calculating the percentage error of the meter under test under the representative real load conditions, and displaying such representative error as a percentage.